It is common for more than one well to be drilled in, through or about a reservoir. With the advent of processing systems and data analysis techniques, it is frequently advantageous to use interference and/or pulse testing to determine information about underground formations of the reservoir. For example, interference testing may be performed between pairs of wells where the monitor and/or pulsing well may be horizontal or vertical. In the case of horizontal wells, interference testing may predominantly provide areal connectivity information. In the case of vertical wells, interference testing may predominantly provide vertical connectivity information. Areal and/or vertical connectivity information may be used to evaluate permeability of the underground formations, and, for example, may be used to determine production strategies for the exploitation of the reservoir.
Obtaining information on geotechnical features using interference testing while drilling has been limited by communication difficulties between downhole tools and the surface. Conventionally, mud pulse telemetry is by far the most often used of the few techniques in commercial use for communication while drilling, between downhole equipment and the surface, thus problems remain in the industry. Unless otherwise indicated, references, throughout, to “while drilling,” or the like, are intended to mean that the drill string is in the borehole or partially in the borehole as part of an overall drilling operation including drilling, pausing, and or tripping, and not necessarily that a drill bit is rotating.
In mud pulse telemetry, for example, data is transmitted as pressure pulses in the drilling fluid. Mud pulse telemetry, however, has well known limitations, including relatively slow communication, low data rates, and marginal reliability. Current mud pulse technology is capable of sending downhole data at only about twelve (12) digital bits per second. In many cases, this rate is insufficient to send all the data that is required to make real-time data acquisition and tool operating decisions, or this rate is limiting on the configuration of a desired tool string. Also, mud pulse technology does not work well in extended reach boreholes. Signaling from uphole to downhole, by regulating mud pump flow, in order to control processes such as directional drilling and tool functions, is also slow, and has a very low data transfer rate. Also, under certain circumstances, for example underbalanced drilling employing gases or foamed drilling fluid, current mud pulse telemetry systems cannot function.
There have been various attempts over the years to develop alternatives to mud pulse telemetry that are faster, have higher data communication rates, and do not require the presence of a particular type of drilling fluid. For example, acoustic telemetry has been proposed, which transmits acoustic waves through the drill string. Data communication rates are estimated to be approximately an order of magnitude higher than mud pulse telemetry, but these increased data communication rates are still limiting. Moreover, noise is a problem in these conventional systems. Another example is electromagnetic telemetry through the earth. This technique is considered to have limited range and depends on characteristics, especially resistivity, of the formations surrounding the borehole.
As alternative configuration, the placement of wires in drill pipes has been proposed to increase the data transmission rate. This proposal will carry signals throughout the drill pipe. Some early approaches to a wired drill string are disclosed in: U.S. Pat. No. 4,126,848, U.S. Pat. No. 3,957,118 and U.S. Pat. No. 3,807,502, and the publication “Four Different Systems Used for MWD,” W. J. McDonald, The Oil and Gas Journal, pages 115-124, Apr. 3, 1978.
The idea of using inductive couplers, such as at the pipe joints, has also been proposed as another alternative. The following documents disclose use of inductive couplers in a drill string: U.S. Pat. No. 4,605,268, Russian Federation published patent application 2140527, filed Dec. 18, 1997, Russian Federation published patent application 2040691, filed Feb. 14, 1992, and WO Publication 90/14497A2, Also see: U.S. Pat. No. 5,052,941, U.S. Pat. No. 4,806,928, U.S. Pat. No. 4,901,069, U.S. Pat. No. 5,531,592, U.S. Pat. No. 5,278,550, and U.S. Pat. No. 5,971,072.
U.S. Pat. No. 6,641,434 to Boyle et al. and U.S. Pat. No. 6,866,306 to Boyle et al., both assigned to the assignee of this application and incorporated by reference in their entirety, describe a wired drill pipe joint that is a significant advance in the wired drill pipe art for reliably transmitting measurement data in high-data rates, bidirectionally, between a surface station and locations in the borehole. The '434 and the '306 patents disclose a low-loss wired pipe joint in which conductive layers reduce signal energy losses over the length of the drill string by reducing resistive losses and flux losses at each inductive coupler. The wired pipe joint is robust in that it remains operational in the presence of gaps in the conductive layer. The performance attendant to these and other advances in the drill string telemetry art provides opportunity for innovation where prior shortcomings of range, speed, and data rate have previously been limiting on system performance.
Interference tests in established/producing reservoirs are often difficult to conduct and delicate measurements have to be performed under optimal circumstances. Very sensitive pressure gauges are placed in a quiet environment that is carefully controlled in order to measure the (invariably) small pulses induced by perturbing the production or injection schedule at a remote well. The pulse can take (many) hours, days, months and even years to develop and may be so smeared out that it is virtually indistinguishable from a background trend. The drilling environment tends to be very noisy so it is necessary to try and maximize the signal-to-noise ratio even though it may be very unfavorable.